The present invention relates generally to UV (ultraviolet) photosensitive bulk glass, and particularly to batch meltable alkali boro-alumino-silicate glasses. The photosensitive bulk glass of the invention exhibits photosensitivity to UV wavelengths below 250 nm.
The photosensitivity of the alkali boro-alumino-silicate bulk glass to UV wavelengths below 250 nm provides for the making of refractive index patterns in the glass. With a radiation source below 250 nm, such as a laser, refractive index patterns are formed in the glass. The inventive photosensitive optical refractive index pattern forming bulk glass allows for the formation of patterns in glass and devices which utilize such patterned glass.
In a particular embodiment the photosensitivity of the inventive bulk glass is utilized to make Bragg gratings in the glass. As described in the U.S. Patent Application Serial No. 60/221,770, filed Jul. 31, 2000, Bulk Internal Bragg Gratings and Optical Devices, the inventive photosensitive bulk glass is particularly suited for the making of photonic devices utilized in optical telecommunications.
The invention includes a photosensitive glass. The starting glass is a photosensitizable alkali boro-alumino-silicate glass that can be loaded with hydrogen to make it photosensitive. Preferably the glass is a below 250 nm photosensitive glass which has a composition of 40-80 mole % SiO2, 2-15 mole % GeO2, 10-36 mole % B2O3, 1-6 mole % Al2O3 and 2-10 mole % R2O where R is chosen from the alkali elements with the glass exhibiting photosensitivity to below 250 nm wavelengths.
The invention further includes a molecular hydrogen loadable photosensitive bulk glass. The photosensitive bulk glass is an alkali boro-alumino silicate glass with a melting temperature no greater than 1650xc2x0 C. Preferably the glass has a batch composition comprising no greater than 85 mole % SiO2, no less than 10 mole % B2O3, no less than 2 mole % GeO2, and a combined alkali and alumina content no greater than 20 mole % Al2O3+Alkali with the glass having a molecular hydrogen loadable level of at least 1018 H2 molecules/cm3.
The invention further includes a method of making a refractive index pattern. The invention includes providing a photosensitive bulk glass having a 250 nm absorption less than 20 dB/cm, providing a radiation source below 250 nm, forming a pattern with the below 250 nm radiation, and exposing the photosensitive bulk glass to the pattern to form a modulated refractive index pattern in the bulk glass.
The invention further includes a method of making a molecular hydrogen loadable photosensitive glass optical device preform. Preferably the method comprises making a refractive index pattern preform out of melted glass. The method includes providing a germania silica glass powder batch with a transition metal contamination levelxe2x89xa61 ppm by weight for transition metals and a heavy metal contamination levelxe2x89xa61 ppm by weight for heavy metals. The method includes melting the silica glass powder batch to form a homogeneous glass melt, cooling the glass melt into a UV transmitting bulk glass having a 250 nm absorption less than 20 dB/cm and forming the bulk glass into an optical device preform in which refractive index patterns can be made.
The invention further includes a photosensitive glass optical refractive index pattern preform for use with UV light in the formation of refractive index patterns. The preform is comprised of an Alkali boro-alumino-silicate glass with a 250 nm absorption less than 20 dB/cm. The preform glass has a UV wavelength inducable modulated refractive index xcex94n level greater than 10xe2x88x925 with a molecular hydrogen level of at least 1018 H2 molecules/cm3.